bug#64928: 29.1; format-decode-buffer fails for de646 and duden

[Eli Zaretskii]

> From: Ulrich Müller <ulm@gentoo.org>
> Date: Sat, 29 Jul 2023 12:52:40 +0200
> 
> The following command results in an error:
> 
> M-x format-decode-buffer RET de646 RET
> Format decoding failed
> recode: Request `iso646-ge:latin1' is erroneous
> 
> The "duden" encoding does not work either:
> 
> M-x format-decode-buffer RET duden RET
> Format decoding failed
> /bin/bash: line 1: diac: command not found
> 
> A trivial patch is included below.
> 
> (Not sure if fixing this is even worth the effort. AFAICS Recode never
> recognised a charset "iso646-ge". The ISO 646 variants were added
> in 1993 with recode-3.3, and its label for the German variant was
> "iso646de" even back then. So nobody has reported this since almost
> 30 years.)

I see no harm in installing this on master.

Thanks.